Biology Reference
In-Depth Information
where irreversible attachment to the protein matrix via a histidine linkage
occurs under certain conditions (
Vu, Jones, & Lecomte, 2002; Vu,
Vuletich, Kuriakose, Falzone, & Lecomte, 2004
). This feature, discovered
in 2002, is likely to represent a response to specific metabolic needs. Endog-
enous hexacoordination and covalent attachment illustrate original ways in
which haem reactivity can be co-opted to condition globin function. Since
it was first observed, the unusual chemistry supported by T globins has been
the subject of several studies and has fostered new functional hypotheses.
Few laboratories are actively engaged in the study of algal and cyan-
obacterial globins. Although information becomes occasionally available
as a by-product of other investigations such as global gene expression studies,
much dedicated work will be necessary to mine the rich chemical and
functional landscape these proteins have to offer.
3. PHYLOGENY
3.1. Tying photosynthesis to cyanobacterial
and algal globins
The cyanobacteria and algae considered here are first and foremost photo-
synthetic organisms. During photosynthesis, they are actively extracting
electrons from water and generating molecular oxygen within cellular com-
partments undergoing rapid metabolism. Given the probable role of certain
cyanobacterial globins in mitigation of reactive oxygen and nitrogen mole-
cules (reactive oxygen species (ROS)/reactive nitrogen species (RNS);
Hill
et al., 1996; Scott et al., 2010; Smagghe, Trent, & Hargrove, 2008
), recog-
nition of the photosynthesis occurring in these cells seems essential for a finer
definition of relevant activities. Within this context, it is also important
to stress that although cyanobacteria and algae are both photosynthetic,
they possess distinctive physical characteristics and do not utilize identical
machineries.
Cyanobacteria are photosynthetic bacteria commonly referred to as
blue-green algae. Although the term 'algae' can be, and is, applied to a wide
variety of aquatic organisms, in this discussion we will use the term cyano-
bacteria to highlight the prokaryotic lineage of these organisms. Likewise,
we will define 'algae' as selectively referring to the green algae (as discussed
below). As prokaryotes, cyanobacteria lack specialized compartments such as
the chloroplasts of eukaryotes, but do have dedicated membranes for pho-
tosynthesis called thylakoids (
Beck, Knoop, Axmann, & Steuer, 2012;
Vothknecht & Westhoff, 2001
). Cyanobacteria are found in virtually every
